U.S. Severe Weather Forecast (Coup d'œil sur la convection)

Day Three

acus01 kwns 200039 
Storm Prediction Center ac 200037 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0637 PM CST Friday Dec 19 2014 

Valid 200100z - 201200z 

..no thunderstorm areas forecast... 

thunderstorms are not expected over the lower 48 states tonight. 

..cntrl Gulf Coast... 
A shortwave trough located over adjacent portions of Arkansas/OK/TX this 
evening will weaken as it continues to move east-northeastward to the Tennessee Valley 
and southern Appalachians by Saturday morning. Surface high pressure 
leading to generally tranquil conditions will influence much of the 
area east of The Rockies. The exception will be a light rain shield 
over the central Gulf Coast states tonight. Appreciable buoyancy will 
likely remain offshore the central Gulf Coast and thunderstorms are 
not forecast for tonight. 

.Smith.. 12/20/2014 

Mesoscale Discussion

acus11 kwns 170924 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170924 

Mesoscale discussion 1980 
National Weather Service Storm Prediction Center Norman OK 
0324 am CST Wednesday Dec 17 2014 

Areas affected...portions of coastal Southern California 

Concerning...severe potential...watch unlikely 

Valid 170924z - 171130z 

Probability of watch issuance...5 percent 

Summary...limited risk for a marginally damaging wind gust or two -- 
or possibly a brief/weak tornado -- is evident over coastal portions 
of Ventura/Los Angeles/Orange counties in Southern California early this morning. 
Ww issuance will not be required. 

Discussion...latest radar and lightning data depict a small cluster 
of thunderstorms crossing The Channel islands area and adjacent 
coastal Southern California at this time...coincident with a middle-level cyclonic 
circulation center moving east-southeastward across this area per WV loop. 

Despite surface dewpoints only in the low 50s...relatively steep 
lapse rates through the lower and middle troposphere are 
contributing to marginal cape /a few hundred j/kg per objective 
analyses/...thus fueling updrafts which are extending through the 
mixed-phase /-20 c/ layer. 

While area vwps depict relatively modest /20 to 30 knots/ swlys through 
500 mb...backed/sely low-level winds ahead of the storms seem to be 
aiding in occasional weak/short-lived low-level circulations in 
stronger cells -- as observed by kvtx /Ventura/ WSR-88D. Given the 
sustained/weakly rotating storms...a very isolated/low-end severe 
risk may spread onshore over the next couple of hours. With that 
said...any risk for strong winds and/or a brief/weak tornado should 
remain well below thresholds required to consider ww issuance. 

.Goss/Thompson.. 12/17/2014 

..please see www.Spc.NOAA.Gov for graphic product... 


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